Calculus Word Problem

A plane flies horizontally at an altitude of 6 km and passes directly over a tracking telescope on the ground. When the angle of elevation is pie/3, this angle is decreasing at a rate of pie/6 rad/min. How fast is the plane traveling at that time? (Round your answer to two decimal places.)

A plane flies horizontally at an altitude of 6 km and passes directly over a tracking telescope on the ground. When the angle of elevation is pie/3, this angle is decreasing at a rate of pie/6 rad/min. How fast is the plane traveling at that time? (Round your answer to two decimal places.)

did you make a sketch ?

let = horizontal distance the plane travels

take the derivative w/r to time, substitute in your given and calculated values, then determine the value of